1. Field of the Disclosure
The disclosure relates generally to polyimide particles and powders as well as to methods for the production thereof. More specifically, the disclosure relates to polyimide particles and powders, which dissolve rapidly in solvents and in polymers, such as epoxy, and methods for the production of such particles and powders.
2. Description of the Related Art
The addition of high heat thermoplastics like polyetherimide to epoxy materials enhances the toughness of the matrix while preserving other mechanical properties. Micronized polyimide powders, such as polyetherimide powders are used as additives for many products, because they can impart useful product attributes. A polyimide powder, for instance, can serve as thermoplastic impact modifier, can improve the toughness of bismaleimide (BMI) and/or epoxy, can impart high temperature resistance properties, can provide low moisture uptake, can provide improved Fire, Smoke and Toxicity (FST) properties, and provide excellent metal adhesion properties.
To improve the rate of dissolution of thermoplastics in composite materials, the industry follows one of two methods. First, a thermoplastic polymer can be dissolved in an organic solvent, such as methylene chloride. The resulting solution can be mixed into an epoxy material. The solvent is removed after epoxy and thermoplastic material are thoroughly mixed. See: Die Angewandte Makromolekulare Chemie 213 (1993) 93-111 (Nr. 3715), which is incorporated by reference in its entirety. Second, the thermoplastic polymer can be mechanically ground to a very fine particle size, for example, less than 100 microns or preferably less than 45 microns. Subsequently, the resultant micronized powder is dissolved in epoxy material. See: U.S. Pat. No. 7,592,072, which is incorporated by reference in its entirety.
Polyimide powders made by cryo-grinding, jet milling processes, emulsion processes, and mechanical grinding processes take too long to dissolve in solvents and polymers, such as epoxies. Additionally such fine polyimide powders can have a high conversion cost, involve dusting, dust inhalation, and/or explosion hazard as well as other materials handling difficulties. Therefore, such fine powders are often not desirable.
For the foregoing reasons, there is a need for particles that do not cause high conversion costs, nor require specialized material handling and dust inhalation precautions while simultaneously providing faster dissolution of thermoplastics in epoxy medium. Meeting this need would result in shorter cycle time and cost savings.